This invention relates to the communication of audio signals over A.C. power and wiring lines and, more particularly, to a so-called wireless remote system by which stereophonic signals may be transmitted from, for example, hi-fidelity audio equipment to loudspeakers.
The technique of using the A.C. wiring system in a home or office to serve as the transmission medium for audio signals has long been used. One application of this technology is the widely available wireless intercom system which allows individuals in different rooms of a house to converse with one another. Unfortunately, conventional wireless intercom systems have met with less than enthusiastic acceptance.
Typical wireless intercom systems rely on A.M. transmitting and receiving principles and, consequently, are susceptible to electromagnetic noise which degrades the audio signal. The A.C. power lines in most households are subjected to electromagnetic noise from many sources. It is common, therefore, for the A.M. signals transmitted over such lines to be so degraded that the information contained therein is not comprehensible when received. While careful design considerations in wireless intercoms might succeed in overcoming this difficulty, presently available intercom devices tend to be inexpensively constructed and/or designed. Noise reducing circuits, if present, usually fail to provide adequate noise immunity.
With these problems in mind, it is readily apparent that existing wireless intercom techniques cannot be turned to account for the transmission of high fidelity audio signals through household A.C. power lines.